1. Field of the Invention
The present invention relates to a power plug with plug terminals provided rotatably with respect to a housing.
2. Description of the Prior Art
Some chargers for a portable electric device have a power plug having a pair of plug terminals that can rotate between a projecting position, where tips thereof project from a housing made of synthetic resin, and an accommodated position, where the tips are housed in an accommodation part of the housing. When using such a charger, the plug terminals are brought to their projecting position for insertion into an outlet. When the charge is not used, however, the plug terminals can be accommodated in the housing so as to be out of the way.
Such power plugs include one disclosed in Japanese Patent No. 3096896. In this plug, a pair of plug terminals are held by bases thereof embedded into a rotation shaft member made of synthetic resin, and the rotation shaft member is rotatably supported on the housing. By rotating the rotation shaft member, the plug terminals are displaced from the accommodated position, where they are accommodated in the housing, to the projecting position, where they project from the housing. The housing has a pair of elastic pieces, opposed to each other, that are provided integrally therewith near the rotation shaft member. The rotation shaft member has an engagement pin in the shape of a round bar, and the engagement pin enters into a gap between the pair of elastic pieces as the rotation shaft member rotates. The engagement pin expands the gap between the elastic pieces while entering therein and is held in that position. Thus, the plug terminals are held in the projecting position thereof.
However, in the above described arrangement in which the round-bar-like engagement pin enters by force into the gap between the elastic pieces, a significant displacement of the elastic pieces cannot be set, and a sufficient touch of a click cannot be provided. To enhance the touch of a click, it is necessary to upsize the engagement pin or the like. However, due to the restriction on the overall size of the power plug, the upsizing of the engagement pin or the like is also restricted.
This invention has been developed in view of the above described circumstances, and an object thereof is to provide a power plug capable of providing a firm and steady touch of a click.
According to the present invention, a rotation shaft for integrally supporting a set of plug terminals is received on a bearing of a housing. Thus, the plug terminals are supported rotatably with respect to the housing. The rotation shaft comprises a prismatic bar with a peripheral surface including a plurality of plane surfaces and ridges between the plane surfaces, and a pair of elastic pieces positioned to sandwich the rotation shaft therebetween is brought into contact with the plurality of plane surfaces of the prismatic bar. The pair of elastic pieces are arranged not to rotate with the rotation shaft and, as the rotation shaft rotates, are elastically deformed to expand by pressure from the ridge of the prismatic bar. Here, when the rotation shaft is rotated by rotating the plug terminals, the ridges of the prismatic bar press the elastic pieces outwardly. Therefore, the distance between the elastic pieces is repeatedly increased and decreased with the rotation of the rotation shaft. A firm and steady touch of a click is provided when the rotation shaft rotates from a first angle position, where the distance between the elastic pieces is the narrowest, to a second angle position where the distance becomes the narrowest once it has become the widest.
In such an arrangement, a large displacement of the elastic pieces can be set according to the cross-section of the prismatic bar, and a more obvious touch of a click can be provided compared to a prior art arrangement in which the round-bar-like engagement pin simply enters into the gap between a pair of elastic pieces.
Furthermore, in the case where the plug terminals are locked at an angle of 90 degrees as in the prior art arrangement described above, the cross-section of the prismatic bar is preferably formed into a square shape. In such an arrangement, the increase and decrease in the distance between the elastic pieces are repeated every 90 degrees of rotation, so that the plug terminals can be rotated with a simple angle interval to provide a touch of a click.
In addition, the elastic pieces are preferably formed as parts separate from the housing and mounted on the housing in a detention state.
In the prior art arrangement described above, in which the elastic pieces are formed integrally with the housing made of resin, it may be difficult to select a material for the elastic pieces that has a sufficient strength, such as elasticity, wear resistance and rigidity, or to form the material into a shape with these properties. Therefore, by separating the elastic pieces from the housing, an appropriate material can be used for the elastic pieces, or the elastic pieces can be readily formed into an optimal shape.